When filling material such as sausage meat, putty or sealing compound is fed through a filling tube coupled to a filling machine into a tubular casing closed at one end, a sausage is formed at the filling tube exit. The casing, which was previously pulled onto the filling tube either manually or automatically or which was produced in situ from a flat web of film folded and sealed over the filling tube to form a tube, is pulled off the filling tube by the filling pressure.
The retention device of the kind initially described and adequately known to those in the art is stationarily disposed adjacent the filling tube during filling and is configured to serve as a holding and support means for a brake ring (also known as a casing brake) clasped around the filling tube. The retention device thus comprises a support bracket (casing brake holder) that is generally suitable for receiving brake rings of different diameters in order to allow adaptation to different filling tube diameters. The brake ring, which typically includes an annular rubber lip, is elastically biased against the filling tube. As a result of this bias, it presses the casing against the filling tube. This pressure generates the frictional pressure which ensures that the casing is drawn from the filling tube in a controlled manner during the filling process and that, depending on the bias of the brake ring, a sausage with the desired fullness is produced.
Located downstream from the filling device comprising the filling tube and the retention device is a device for partitioning portion packs, a so-called clip machine, which constricts the filled casing using displacement elements (referred to in brief as “displacers”), thus displacing any filling material located in the constricted portion, before one or two closure elements known as clips are then placed on the constricted portion (gathered end or tress) of the casing and closed around it by closing tools. The casing can be severed between the two clips with a knife to selectively produce either separate sausages or strings of sausages of a desired length. Two kinds of partitioning and closing devices are known: firstly, those with spreading displacement, in which after closure the displacement elements are axially moved apart in relation to the tubular casing in order to lengthen the constricted portion so that the clips can be applied. A casing partitioning and closing device that dispenses with extended tress formation in favour of simpler kinematics is known, secondly, from DE 101 31 807. This type of casing partitioning and closing device can operate at substantially higher clock rates due to its simpler kinematics.
It is known in connection with spreading displacement to retract the brake ring on the filling tube during spreading into a released position, in the opposite direction to the direction that the tubular casing is pulled off the filling tube. This is necessary in order to free a sufficient volume of the packaging into which the filling material displaced when the displacement elements are spread for closure can then escape. In the prior art, this is achieved by coupling the casing brake holder to a pneumatic drive that acts in a direction parallel to the filling tube and which retracts the brake ring together with the support bracket on the filling tube while the displacers constrict and spread the gathered end of the casing. When the partitioning and closing operation has been completed, the pneumatic drive moves the brake ring forwards again when the next filling cycle of the intermittently operating filling device begins, into a forward position close to the exit opening of the filling tube, thereby wiping the previously displaced filling material into the new tubular casing being pulled off. Partitioning and closing devices with spreading displacement usually operate at clock rates of 50 to 100 operating cycles per minute.
However, closing devices such as the portioning device known from DE 101 31 807 are unable to increase the production speed to any considerable extent. At clock rates greater than 200 cycles per minute, synchronicity and a sufficient stroke length of the back-and-forth movement of the pneumatic linear drive are no longer assured, because the working medium (air or other fluid) does not flow fast enough—in any case when the feed lines have normal dimensions—even when the valves of the pneumatic drive are precisely timed. For this reason also, extended tress formation by means of spreading displacement is dispensed with these clip machines, because not as much filling material is then displaced, and because it is also possible to dispense with any yielding movement on the part of the brake ring.